The present invention generally relates to facsimile machines, and more particularly to a facsimile machine which has a function of retransmitting an image data when a transmission error is detected.
Conventionally, there are facsimile machines which transmit an image data in conformance with an error correction mode (ECM) of a Group III standard recommended by the CCITT. It will be assumed for convenience' sake that one page of a document shown in FIG. 1A is read on a source facsimile machine. When coded data dl through dn of first through nth lines are obtained, an end of line (EOL) code indicating an end of a line is added to each of the coded data dl through dn. The EOL code is used for synchronizing each line. According to the ECM, the 256 bytes or 64 bytes of the image data are set at a time into a high level data link control (HDLC) frame having a predetermined format, and a maximum of 256 frames are transmitted as one block of the image data.
A destination facsimile machine checks a data error in the received image data for each frame, and sends back a retransmission request to the source facsimile machine when a data error is detected so as to request a retransmission of a frame in which the data error exists. Hence, the source facsimile machine retransmits the image data of the requested frame in response to the retransmission request.
Recently, a facsimile communication is made through a mobile telephone set and a multi channel access (MCA) radio telephone set. In such a case, a radio line is used for the facsimile communication and thus a transmission error easily occurs when the state of the radio line deteriorates. Accordingly, when the facsimile communication is made in the ECM under such a condition, it becomes necessary to repeatedly retransmit the image data many times.
Generally, a data transmission rate is shifted down in the ECM every time the retransmission is repeated three times. When the retransmission is repeated three times at a minimum data transmission rate of 24000 bps, the facsimile transmission is ended. On the other hand, when the transmission is unsuccessful even when the same frame is retransmitted three times, the retransmission of this frame is discontinued and a next predetermined transmission is made such as transmitting an end signal in conformance with a protocol of the facsimile machine.
It will be assumed that the destination facsimile machine receives one page of the document in one block and the transmission of a specific frame f.sub.s is discontinued, for example. In this case, the image amounting to this specific frame f.sub.s is not recorded, but instead a blank or space, for example, is formed at a position of the erroneous frame which contains the data error as shown in FIG. 1B. Line information of a large number of lines are transmitted within one frame, but conventionally, the image corresponding to the entire frame drops out even when the data error occurs in only one line of the frame. Thus, there is a problem in this case that a length L.sub.1 of the recorded image shown in FIG. 1B recorded on the destination facsimile machine is greatly reduced compared to a length L.sub.0 of the original image shown in FIG. 1A transmitted on the source facsimile machine.
On the other hand, according to the ECM, one block of the image data has a data quantity of 64 kbytes when one frame has 256 bytes because one block has a maximum of 256 frames. In a case where the image data of one page of the document exceeds the data quantity of one block, this one page of the document is transmitted in divisions in a plurality of blocks as partial pages. For example, when one page of the document is transmitted in divisions in two partial pages, the retransmission may be ended during the transmission of a first partial page in a state where the error correction is not completed. In such a case, the image not only drops out in a first half of one page as shown in FIG. 1C but a latter half of this page will not be received, and there is a problem in that one page of the document cannot be recorded.